Tue·Nov 6, 2007Tuesday·November 6, 2007

1. 01*

   A Schur Complement Approach to Chiral Fermions

   Artan Borici🇦🇱

   Lattice chiral fermions are synonymous to the Ginsparg-Wilson relation. Indeed, this relation is satisfied by the overlap, domain wall and perfect action fermion kernel. In a recent work we have shown that it is possible to take a direct RG approach for fermions in the presence of gauge fields. This is due to an algebraically implicit blocking technique which yields a Schur-complementary coarse Dirac operator. Using a Schur complement approximation which is stable and regular, the scheme can be iterated to the fixed point. In this talk, we elaborate more on the direct RG approach and show how to get highly improved chiral fermions on the coarse lattice with the gauge fields remaining on the fine lattice. We give numerical examples in the case of lattice QCD using QCDLAB {\tt http://phys.fshn.edu.al/qcdlab.html}

   hep-latPoS(2007)·3 citations
2. 02*

   Comparing Pure Yang-Mills SU(2) and SU(3) Propagators

   Attilio Cucchieri · Tereza Mendes. Orlando Oliveira · Paulo J. Silva

   The infrared behavior of gluon and ghost propagators in Yang-Mills gauge theories is of central importance for the understanding of confinement in QCD. While analytic studies using Schwinger-Dyson equations predict the same infrared exponents for the SU(2) and SU(3) gauge groups, lattice simulations usually assume that the two cases are different, although their qualitative infrared features may be the same. We carry out a comparative study of lattice (Landau) propagators for both gauge groups. Our data were especially produced with equivalent lattice parameters to allow a careful comparison of the two cases.

   hep-latIJMPE(2007)·2 citations
3. 03*

   Revisiting the pentaquark episode for lattice QCD

   A.S.B. Tariq🇧🇩

   This work revisits the pentaquark episode, particularly in reference to lattice QCD, to collect in one place the lessons that have been or should be learnt. This also examines whether, and if yes, where, there might be any prospect for future studies of pentaquarks and the role of lattice QCD in it. Tests such as volume dependence, and hybrid boundary conditions to distinguish bound and scattering states are identified as the positives to take forward from this episode. On the other hand it is also observed that pentaquarks with heavier quark content and in the $SU(3{)}_f$ limit may still be worth not forgetting, and in that case lattice QCD may have an important role to play.

   hep-lathep-phPoS(2007)·8 citations
4. 04*

   Formulating Light Cone QCD on the Lattice

   D. Grunewald🇩🇪 · E.-M. Ilgenfritz🇩🇪 · E.V. Prokhvatilov🇷🇺 · H.J. Pirner🇩🇪

   We present the near light cone Hamiltonian $H$ in lattice QCD depending on the parameter $\eta$, which gives the distance to the light cone. Since the vacuum has zero momentum we can derive an effective Hamiltonian $H_{eff}$ from $H$ which is only quadratic in the momenta and therefore solvable by standard methods. An approximate ground state wave functional is determined variationally in the limit $\eta \to 0$.

   hep-lathep-thPRD(2008)·13 citations
5. 05*

   Excited hadrons on the lattice - State of the art and future challenges

   Christof Gattringer (Graz)🇦🇹

   We review the techniques of lattice QCD calculations for excited hadrons with light quarks and outline the future challenges that are faced in calculations with fully dynamical fermions.

   hep-lathep-phnucl-th11 citations
6. 06*

   Distributions of individual Dirac eigenvalues for QCD at non-zero chemical potential: RMT predictions and lattice results

   Gernot Akemann🇬🇧 · Jacques Bloch🇩🇪 · Leonid Shifrin🇬🇧 · Tilo Wettig🇩🇪

   For QCD at non-zero chemical potential $\mu$, the Dirac eigenvalues are scattered in the complex plane. We define a notion of ordering for individual eigenvalues in this case and derive the distributions of individual eigenvalues from random matrix theory (RMT). We distinguish two cases depending on the parameter $\alpha ={\mu }^2{F}^{2}V$, where $V$ is the volume and $F$ is the familiar low-energy constant of chiral perturbation theory. For small $\alpha$, we use a Fredholm determinant expansion and observe that already the first few terms give an excellent approximation. For large $\alpha$, all spectral correlations are rotationally invariant, and exact results can be derived. We compare the RMT predictions to lattice data and in both cases find excellent agreement in the topological sectors $\nu =0,1,2$.

   hep-latPoS(2007)·3 citations
7. 07*

   Recent lattice results on finite temperature and density QCD, part I

   Frithjof Karsch🇺🇸

   We discuss recent progress made studies of bulk thermodynamics of strongly interacting matter through lattice simulations of QCD with an almost physical light and strange quark mass spectrum. We present results on the QCD equation of state at vanishing and non-vanishing quark chemical potential and show first results on baryon number and strangeness fluctuations, which might be measured in event-by-event fluctuations in low energy runs at RHIC as well as at FAIR.

   hep-lathep-phPoS(2007)·65 citations
8. 08*

   Recent lattice results on finite temerature and density QCD, part II

   Frithjof Karsch🇺🇸

   We discuss recent progress in studies of QCD thermodynamics with almost physical light quark masses and a physical value of the strange quark mass. We summarize results on the transition temperature in QCD and analyze the relation between deconfinement and chiral symmetry restoration.

   hep-lathep-phPoS(2007)·83 citations
9. 09*

   't Hooft vertices, partial quenching, and rooted staggered QCD

   Claude Bernard (Washington U.)🇺🇸 · Maarten Golterman (SFSU)🇺🇸 · Yigal Shamir (Tel-Aviv U.)🇮🇱 · Stephen Sharpe (U. of Washington)🇺🇸

   We discuss the properties of 't Hooft vertices in partially quenched and rooted versions of QCD in the continuum. These theories have a physical subspace, equivalent to ordinary QCD, that is contained within a larger space that includes many unphysical correlation functions. We find that the 't Hooft vertices in the physical subspace have the expected form, despite the presence of unphysical 't Hooft vertices appearing in correlation functions that have an excess of valence quarks (or ghost quarks). We resolve an apparent paradox that arises when one uses rooted staggered fermions to study one-flavor QCD, by showing how, in partially quenched theories, it is possible to have spontaneous symmetry breaking of a non-anomalous symmetry in finite volume. Using these results, we demonstrate that arguments recently given by Creutz--claiming to disprove the validity of rooted staggered QCD--are incorrect. In particular, the unphysical 't Hooft vertices do not present an obstacle to the recovery of taste symmetry in the continuum limit.

   hep-lathep-phPRD(2008)·53 citations
10. 10*

    Lattice gauge theory with staggered fermions: how, where, and why (not)

    Andreas S. Kronfeld🇺🇸

    Many results from lattice QCD of broad importance to particle and nuclear physics are obtained with 2+1 flavors of staggered sea quarks. In the continuum limit, staggered fermions yield four species, called tastes. To reduce the number of tastes to one (per flavor), the simulation employs the fourth root of the four-taste staggered fermion determinant. This talk surveys evidence in favor of this procedure, refutes recent criticisms, and reviews recent algorithmic and technical improvements. Physics results are covered in other plenary talks.

    hep-lathep-phnucl-thPoS(2007)·117 citations
11. 11*

    Confinement, Screening and the Center on S^3 x S^1

    Carlos Hoyos🇬🇧 · Biagio Lucini🇬🇧 · Asad Naqvi🇬🇧

    We compute the one-loop effective potential for the Polyakov loop on $S^{3}times{S}^1$ for an asymptotically free gauge theory of arbitrary group $G$ and a generic matter content. We apply this result to study the phase structures of $G_2$, SO(N) and $Sp(2N)$ gauge theories which turn out to be in qualitative agreement with the results of lattice calculations. On $S^3\times S^1$, at zero temperature, the Polyakov loop is zero for kinematical reasons. For small but non-zero temperature, the Polyakov loop is still zero if the gauge theory has an unbroken center, while it acquires a small vacuum expectation value for gauge theories whose center is trivial or explicitly broken by the presence of dynamical matter fields. At high temperatures, the saddle point structure of the effective potential is different from the low temperature case suggesting that the theory is in the deconfined phase. At finite $N$, the Polyakov loop is non-zero in the high temperature phase only in theories with no unbroken center symmetry, consistent with screening of the external charge introduced by the Polyakov loop and Gauss law on a compact space.

    ↳ hep-thhep-latJHEP(2008)·10 citations

* Reconstructed cohort: no mailing for this day survives in the archive. Papers are grouped by their submission times and arXiv's announcement cut-off, assuming announcement without delay; positions follow identifier order. Validated at ~91% exact-day agreement against the archived era.